Large object inspection systems using high energy X-ray beams to detect potentially harmful or illegal items (i.e., such as contraband, weapons, illegal drugs, and explosives) include RF linear electron accelerators and conversion targets that transform electron beam energy into a high energy X-ray beam with a single energy spectrum, the parameters of which are determined by the accelerated electron energy. The electrons that are directed at the conversion targets of such inspection systems acquire energy during acceleration in RF fields of the systems' RF linear electron accelerators. Typically, these accelerators provide electrons with 120 mA pulse current acceleration to 9 MeV energy. In the acceleration process, both the energy and current of accelerated electrons are kept constant from pulse to pulse. Unfortunately, the black and white images, representing the contents of a container, that are obtained using such high energy X-ray single spectrum beams do not provide for material discrimination of the container's contents by atomic number.
Therefore, there is a need for RF linear electron accelerators providing accelerated electrons with two energy spectra for use in large object inspection systems that enable the discrimination of materials found in objects present in large cargo containers, and for addressing other related issues.